Liquid crystal display devices have come to be used in watches, calculators, various measuring instruments, automobile panels, word processors, electronic organizers, printers, computers, televisions, clocks, advertising display boards, etc. Representative examples of liquid crystal display modes include TN (twisted nematic) mode, STN (super twisted nematic) mode, VA (vertical alignment) mode in which vertical alignment is realized through use of TFTs (thin film transistors), and IPS (in-plane switching)/FFS mode in which horizontal alignment is featured. Liquid crystal compositions used in these liquid crystal display devices are required to be stable against external factors such as moisture, air, heat, and light, exhibit a liquid crystal phase in a temperature range as wide as possible around room temperature, have a low viscosity, and be driven at low voltage. A liquid crystal composition is composed of several to several tens of compounds in order to optimize the dielectric anisotropy (Δ∈) or refractive-index anisotropy (Δn) for individual display devices.
A liquid crystal composition with negative Δ∈ is used in a vertical alignment display and a liquid crystal composition with positive Δ∈ is used in a horizontal alignment display such as TN, STN, or IPS type. In recent years, there has been reports of a driving mode by which a liquid crystal composition with positive Δ∈ is vertically aligned in the absence of applied voltage and display is performed by applying an IPS/FFS-type electric field. There is an increasing need for a liquid crystal composition with positive Δ∈. Meanwhile, low-voltage driving, high-speed response, and wide operation temperature range are pursued in all driving modes. In other words, positive Δ∈ with a large absolute value, a low viscosity (η), and a high nematic phase-isotropic liquid phase transition temperature (Tni) are required. Moreover, based on the setting of Δn×d, which is a product of Δn and a cell gap (d), the Δn of the liquid crystal composition needs to be adjusted within an appropriate range suitable for the cell gap. In addition, when the liquid crystal display device is to be used in a television or the like, high-speed responsiveness is important and thus a liquid crystal composition with a small γ1 is required.
There have been disclosed liquid crystal compositions that use a compound represented by formula (A-1) or (A-2) with positive Δ∈ as a constitutional component of the liquid crystal compositions (PTL 1 to 4); however, these liquid crystal compositions do not have sufficiently low viscosity.
